I have an idea for an open world single player game where every major location is randomly arranged on the map when you start a new play-through. The main objective would be to search for and collect as may abilities as you can scattered throughout the map to gain the power of a god, and challenge the final boss whenever you feel up to the task.
When you start a new game, a cutscene will play where two metaphysical beings named Paragon and Corruption are fighting each other high in the sky. The fight ends with Paragon being defeated, but not before dealing one last critical blow to Corruption. Upon defeat, Paragon breaks apart into several small particles, each one representing an aspect of Paragon's power, and begins falling to the world below. After the scene ends, you will be taken to a character customization screen. Once you finish customizing your character, a short scene will play where the particle containing Paragon's Will is falling to the ground in first person perspective before crashing through the roof of a house and lands on the player character, sleeping in their bed. The perspective switches to the player character as they open their eyes and look up at the small hole in the ceiling. And that is where the game starts.
The game plays in third person perspective and you start off completely powerless beyond your mundane human abilities. You can challenge Corruption from the very beginning just by sleeping in your bed, but unless you have at least some certain abilities you wont be able to hit Corruption at all.
There are other details I could mention, but I feel like I would just be rambling at this point.
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Happiness is the meaning of life,
and life is the meaning of existence.